Lecture 2: Land Use Pressure & Land Degradation Flashcards
(15 cards)
Trends in Sub-saharan Africa
Food Insecurity: Rising globally, with Sub-Saharan Africa worst affected.
Land Conversion: 40 million ha of forest turned into cropland in Sub-Saharan Africa (1992-2015); half was forest.
Deforestation: Mostly in the tropics, threatening climate regulation, hydrological cycles, and biodiversity.
Land Degradation: Existing cultivated lands suffer from degradation pressures.
Subsistence farming
50% of Africa’s workforce in agriculture BUT majority is in subsistence farming
Subsistence farming → minimal surplus, poverty remains high.
Demographics
Rapid population growth increases food demand.
Poverty and subsistence farming → population growth
African population: nearly 5-fold increase from 1960 to 2020.
Changing consumption patterns
Wealth growth leads to higher meat demand.
Meat is land-intensive: major driver of land demand.
Globalised economy
Export-oriented tropical crops → opportunities to smallholder farmers (cf. “cash crops”)
BUT ALSO foreign investment → land grabbing
Deforestation linked to international trade: South America deforested for export…
Most Sub-Saharan deforestation is for domestic use, not export.
Distinction between deforestation (complete land-use change) and forest degradation (partial quality decline).
Farming marginal lands
Agricultural expansion occurs mostly by area, not productivity improvement.
As fertile land becomes scarce, farmers extend cultivation to:
Steep slopes: erosion-prone.
Wetlands: ecologically sensitive.
Poor and degraded soils (Arenosols: sandy; Ferralsols: nutrient-poor; Lixisols: weathered).
Ecologically unfavourable areas (acidic, shallow, dry, or saline soils).
Only about 10% of African agricultural land has very high agronomic potential.
Land degradation
= human induced process which lowers the current/potential capability of land or soil to produce goods or services → associated with ecosystem services
Major soil functions:
biomass production, water filter, ecological, bearing, raw material, archive, physical/cultural heritage, carbon sequestration
Desertification = land degradation in drylands (climate variation + Human impact)
Chemical soil degradation
= decline quality soil: changes in soil chemical behaviour
Nutrient loss from:
* Slash & burn
* Shifting cultivation (e.g. shortened fallow periods)
* Biomass removal: e.g. wood collected for fuel instead of returned to soil
Physical soil degradation
Soil compaction due to overgrazing and trampling by livestock
Soil erosion
= when impact water/wind detaches & removes soil particles: deteriorate soil
Main driver land degradation
Controlled by: topography, soil characteristics, rainfall, land use/vegetation cover, agriculture practices/conservation measures
On site impacts: topsoil loss, gully erosion → lower crop yields
Off site impacts: Decreased water quality, reduced water storage
Vicious Cycle
The interaction between poverty, population growth, and land pressure creates a vicious cycle:
Poor farmers have low yields → forced to farm more land.
Expansion into marginal areas leads to degradation.
Degraded land lowers yields, reinforcing poverty.
Global demand for food, meat, and export crops reinforces this cycle.
Demographic Transition
Encourage fertility decline through:
- Food security improvement.
- Increased education, especially for girls.
- Women’s empowerment and access to reproductive healthcare.
Change is slow due to demographic momentum.
Change in International Demand
Reducing meat consumption can relieve land pressure.
Meat and livestock products are resource-intensive and major contributors to GHG emissions.
Consumer behaviour in high-income countries plays a role in global land demand.
Close the yield gap
Fertilizers: costly and underused in Africa.
* High prices due to poor infrastructure, import dependence.
* Example: fertilizer 82% more expensive in Mali than in Thailand.
Mechanization: increases labour productivity but often inaccessible to smallholders.
Irrigation: potential to buffer rainfall variability; very limited in Africa.
Support needed for smallholders:
* Access to inputs, credit, and extension services.
* Adoption of improved seeds and practices.
Large-scale, commercial farming may reduce land pressure but risks land grabbing.
Soil and Water Conservation (SWC)
Aims to protect soil, reduce erosion, and maintain productivity.
Underlying principles:
* Reduce raindrop impact.
* Enhance water infiltration and retention.
* Slow surface runoff.
* Guide water flow to prevent damage.
SWC practices:
Biological: vegetation cover, crop rotation, agroforestry.
Agronomic: contour tillage, mulching, intercropping.
Structural: terraces, stone bunds, check dams.
E.g. Stone bunds in Ethiopia increased yields and improved soil moisture.
SWC increases resilience to climate variability and improves food security.
